Snowmobile rear suspension unit

ABSTRACT

An improved suspension system for the drive track of a snowmobile that offers wide amounts of suspension travel and yet is compact enough to be positioned internally of the track. The suspension system permits the use of a tubular shock absorber and a surrounding coil spring for both the front and rear portions of the track. Both front and rear suspension systems embody a link arrangement for moving the ends of the shock absorber and spring toward each other upon upward travel of the track relative to the snowmobile body so as to achieve a wider range of damping for a given degree of suspension travel.

BACKGROUND OF THE INVENTION

This invention relates to a snowmobile suspension unit and moreparticularly to an improved suspension unit for the drive belt of asnowmobile.

As is well known, snowmobiles travel over a wide range of territoriesand it is not uncommon for them to encounter unexpected and abruptchanges in terrain. In order to permit good control and yet a relativelysoft ride when travelling over relatively smooth surfaces, it isparticularly desirable to provide a suspension system that affords afairly large degree of suspension travel. However, due to theconstruction and general configuration of a snowmobile, this is notalways possible. Because of the relatively large space taken up by thedrive belt, it has been difficult to provide a suspension system thatwill afford such wide degrees of suspension travel with full controlthroughout the entire range of travel. Although it has been proposed tomount the suspension medium externally of the drive belt, such anarrangement not only unduly widens the body of the snowmobile butfurther places the suspension components in a location where they may bedamaged. In addition, such outboard mounting of the suspension unitsrequires the use of two units, one at each side of the snowmobile, so asto insure against uneven loadings; thus, increasing the cost of theassembly.

It has been proposed, therefore, to provide a suspension system that ispositioned within the area circumscribed by the drive belt. When thesuspension system is so located, however, it is extremely difficult toinsure the desired degree of suspension travel without interference withthe components. Furthermore, in order to permit such internal mountingof the suspension unit, it has been proposed to use torsional, mousetraptype of springs. This type of spring has several disadvantages in thatis has a high degree of hysteresis and, furthermore, may severaly limitsuspension travel.

The conventional type of snowmobile suspension frequently has the springand/or shock absorber mounted at one end directly upon the vehicle body.As a result, all of the suspension loading is directly transmitted tothe body and this requires a robust construction which adds to bothweight and cost. Also, in order to establish a greater suspensiontravel, it is desirable to incoporate a progressive spring rate.However, with conventional snowmobile suspensions, it has beendifficult, if not impossible, to incorporate an arrangement thatprovides a progressive spring rate without the use of high hysteresissprings.

It is, therefore, a principal object of this invention to provide animproved, compact suspension unit for a vehicle such as a snowmobile.

It is another object of the invention to provide a compact snowmobilesuspension unit which may be positioned within the driving track andwhich yet affords a high degree of suspension travel with adequatecontrol throughout the range of travel.

It is yet a further object of this invention to provide an improvedsuspension system for the rear portion of the driving track of asnowmobile or the like.

It is yet another object of this invention to provide a suspensionsystem that reduces loading on the body.

It is yet a further object of the invention to provide a compact,lightweight suspension system that permits the use of low hysteresisspring and which still affords a possibility of having a progressivespring rate.

SUMMARY OF THE INVENTION

This invention is adapted to be embodied in a suspension system for avehicle such as snowmobile or the like comprising a body and a groundengaging track or the like. The susepension system comprises asuspension element having a pair of relatively movable portions that areadapted to resiliently resist such relative movement. Means operativelyinterpose the suspension element between the track or the like and thebody for moving each of the portion of the suspension element inopposite senses relative to the other upon movement of the track or thelike relative to the body for amplifying the motion of the portions ofthe suspension element relative to each other upon movement of the trackor the like relative to the body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view, with a portion broken away, of asnowmobile embodying a drive belt suspension system in accordance withthis invention.

FIG. 2 is a top plan view showing the details of the suspension system.

FIG. 3 is a side elevational view of the suspension system embodied inthe snowmobile.

FIG. 4 is a cross-sectional view taken along the line 4--4 of FIG. 3.

FIG. 5 is a cross-sectional view taken along the line 5--5 of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A snowmobile embodying a suspension system for the drive belt inaccordance with this invention is identified generally by the referencenumeral 11. The snowmobile 11 has a body assembly, indicated generallyby the reference numeral 12. The body assembly 12 may be of any knownconstruction and when it is referred to herein as a "body", it is to beunderstood that this term is intended to encompass a frame, if the body12 incorporates such a frame, or the elements of the body itself.

A pair of front skis 13 are suspended by means of a suspension system14, which may be of any known type, and are operatively coupled forsteering movement to a handlebar assembly 15 in any known manner. Thesnowmobile 11 includes an engine which drives a continuously variabletransmission having an output sprocket 16 which, in turn, drives a drivebelt 17 in a known manner.

The drive belt 17 is suspended relative to the body 12 by means of afront suspension assembly, indicated generally by the reference number18, and a rear suspension assembly, indicated generally by the referencenumeral 19. The front and rear suspension assemblies 18 and 19 areconnected to a pair of spaced guide rails 21 which, in turn, back up thedrive belt 17 in a known manner. The guide rails 21 carry a first pairof spaced rollers 22 that are coupled to the front suspension assembly18 and which engage the drive belt 17 in spaced relationship to theguide rails 21. In a like manner, a series of spaced guide rollers 23are carried by the rear portion of the guide rails 21 and engage therear portion of the drive belt 17.

Referring to the front suspension unit 18, which is shown is most detailin FIGS. 1 through 4, the guide rails 21 carry a pair of hubs 24 inwhich an axle 25 is journaled in any suitable manner. The rollers 22 areaffixed to the outer ends of the axle 25, also in any suitable manner.Between the guide rails 21 a tube 26 is positioned which tube isrotatable supported upon the axle 25. The tube 26 is a portion of aweldment that comprises what may be considered to be a lever meansassembly. This lever means assembly includes a pair of lever-likemembers 27 that are affixed to the tube 26 for pivotal movement with itand which, as will become apparent, act as bellcranks.

The front suspension 18 also includes a fabricated "A" suspension armassembly consisting of a cross tube 28 that is pivotally supported inany suitable manner on the body 12, by means which may include the bolts29. A pair of depending lever portions 31 are each rigidly connected attheir forward ends to the cross tube 28, as by welding. The rearward endof each of the lever portions 31 are also welded to a rearward crosstube 32 which, in turn, is pivotally connected an upstanding projection33 of each of the guide rails 21 in a suitable manner, as by means ofpivots 34.

Intermediate the pivots 29 and 34, each lever portion 31 is formed withan inwardly extending bracket 51 which has a connection by means of apivot pin 52 to a link 53. The lower end of each link 53 is pivotallyconnected to the forwardmost portion of each lever part 27 by means of apivot pin 54. Upon upward movement of the forwardmost portion of thedrive belt 17 and specifically the axle 25 relative to the body 12, thelinks 31 and 53 will cause the levers 27 and associated tube 26 to pivotabout the axle 25.

The pivotal movement of the levers 27 and tube 26 is employed to load asuspension element, indicated generally by the reference numeral 55. Thesuspension element 55 in the illustrated embodiment includes a tubularshock absorber 56 and a surrounding coil spring 57. The upper end of thespring shock absorber element 55 has a mounting portion 58 that ispivotally connected by means of a bolt and nut assembly 59 to a trunion61 that is affixed to the tube 28.

The suspension element 55 and specifically the shock absorber 56includes a piston rod 62 that is pivotally connected between thetrailing arms of the levers 27 in a known manner as by means of a boltand nut assembly 63. This connection also includes a known arrangementfor loading the lower end of the coil spring 57.

It should be readily apparent that upon suspension movement of the guiderails 21 and drive belt 17, the levers 27 will pivot about this axle soas to load the spring 57 and cause the elements of the shock absorber 56to move relative to each other for resiliently supporting and dampingthe front motion of the drive belt 17. By appropriately locating thepivot points of the linkage employed to load the suspension element 55,either a linear rate or a progressive rate may be accomplished. Thecompact assembly permits the suspension unit to be located within thedrive belt 17 and still have a smooth ride with low hysteresis.

Considering now the rear suspension 19 (FIGS. 1-3 and 5), a tube 64spans the upstanding legs of the guide rails 21 and is journaled thereonby means including bolts 65. A welded lever assembly consisting of apair of arms 66 is affixed to the tube 64 and extends generally upwardlytherefrom. The arms 66 are pivotally connected at their outer ends bymeans of a tube 67 to a pair of fabricated bellcranks 68. The bellcranks68 are, in turn, pivotally supported on an axle 69 which is journaled inthe snowmobile frame or body 12. A shaft 72 also extends between and isaffixed to the bellcrank 68 so as to tie them together. A strap 73encircles the shaft 72 and the tube 64 so as to limit the maximum travelof the guide rails 21 relative to the snowmobile body 12 when the body12 is lifted clear of the ground.

The portion of the bellcranks 68 forward of the axle 69 are pivotallyconnected to respective of a pair of links 74 by means of pivot pins 75.The bellcranks 68 may be formed with one or more additional apertures 76so as to permit adjustment of the point of connection of the links 74 tothe bellcrank 66 to alter the ride characteristics as desired.

The forward ends of the links 74 are pivotally connected to levers 77 bymeans of bolts or the like 78. The levers 77 are, in turn, pivotallysupported relative to the snowmobile body 12 by means of a shaft 79. Thelevers 77 are employed to load a suspension element indicated generallyby the reference numeral 81. The suspension element 81 consists of ahydraulic shock absorber 82 and surrounding spring 83. This loading isaccomplished through the bolt 78 which is connected to the suspensionelement 81 in a known manner.

Guide rollers are carried on the axle 69 for engagement with the drivebelt 17. In a like manner guide rollers 85 are supported on the axle 79for also engaging the drive belt 17.

Also affixed to the bellcranks 68 is a weldment 86 which forms a furtherportion of a bellcrank assembly employed to load both ends of thesuspension element 81. For this purpose the weldment 86 is connected ina known manner to the opposite end of the suspension element 81 by meansincluding a bolt 87.

When the rear portion of the drive belt 17 engages an obstruction, theguide rails 21 will be urged upward relative to the body of thesnowmobile body 12. As a result, the links 66 will load the bellcranks68 and cause them to pivot in a counterclockwise direction about theaxle 69 as viewed in FIG. 3. This pivotal movement will cause the links74 to be drawn rearwardly and pivot the levers 77 also in acounterclockwise direction about the axle 79. As a result of thismovement, the spring 83 and rod of the shock absorber unit 82 will beurged to the right. At the same time, the weldment 86 will be pivotedwith the bellcranks 68 and this motion is transmitted through the bolt87 to cause a the righthand side of the spring 83 and the cylinder unitof the shock absorber 82 to be moved to the left. Thus, the amount ofsuspension travel is amplified at the suspension element 81 so as toprovide in effect a greater rate of travel than would be possible ifonly one end of the suspension assembly 81 were moved when a load wasencountered. Thus, this provides an arrangement whereby less linkage isemployed, a compact assembly results and unsprung weight is reduced. Thelinkage arrangement employed also reduces the amount of suspensionloading which must be borne by the body and, thus, permits a lighterweight construction to be employed. Furthermore, a relatively simplelinkage system is employed to achieve these results and which permit, ifdesired, a progressive spring rate with the use of a low hysteresis typespring, such as the coil springs employed.

It is to be understood that both front and rear suspension units havebeen described for the same drive belt. However, it is possible toemploy either of the suspension units without the other or withdifferent types of suspension units. Various other changes andmodifications may be made without departing from the spirit and scope ofthe invention, as defined by the appended claims.

We claim:
 1. A suspension system for a vehicle such as a snowmobile orthe like comprising a body and a ground engaging track or the like, saidsuspension system comprising a suspension element having a pair ofrelatively movable portions adapted to resiliently resist such relativemovement, and means for operatively interposing such suspension elementbetween said track or the like and said body for moving each of saidportions of said suspension element in opposite senses relative to theother upon movement of said track of the element relative to the bodycomprising a bellcrank having an intermediate pivot support and havingopposite arms each operatively connected to a respective of thesuspension element portions for movement of said portions each in adirection to load said suspension element upon pivot movement of saidbellcrank, and means for pivoting said bellcrank upon movement of saidtrack or the like relative to said body.
 2. A suspension system as setforth in claim 1 wherein the bellcrank is pivotally supported by thebody.
 3. A suspension system for a vehicle such as a snowmobile or thelike comprising a body and a ground engaging track or the like, saidsuspension system comprising a suspension element having a pair ofrelatively movable portions adapted to resiliently resist such relativemovement, and means for operatively interposing such suspension elementbetween said track or the like and said body for moving each of saidportions of said suspension element in opposite senses relative to theother upon movement of said track of the element relative to the bodycomprising a bellcrank having an intermediate portion pivotallysupported by the body and having opposite arms, a link pivotallyconnected to one of said bellcrank arms, a lever pivotally supportedrelative to said body, said link having a pivotal connection to saidlever, one portion of said suspension element being pivotally connectedto said lever and means for operatively connecting the other of saidbellcrank arms to the other of said suspension element portions.
 4. Asuspension system for a vehicle such as a snowmobile or the likecomrising a body and a ground engaging track or the like, saidsuspension system comprising a suspension element having a pair ofrelatively movable portions adapted to resiliently resist such relativemovement, and means for operatively interposing such suspension elementbetween said track or the like and said body for moving each of saidportions of said suspension element in opposite senses relative to theother upon movement of said track of the element relative to the bodycomprising a bellcrank having an intermediate pivot support upon saidbody and having opposite arms each operatively connected to a respectiveof the suspension element portions, and link means pivotally connectedat one end thereof for movement with the track or the like an pivotallyconnected to the other end thereof to said bellcrank.
 5. A suspensionsystem as set forth in claim 4 wherein the means for connecting one ofthe bellcrank arms to one of the suspension element portions includes alink pivotally connected to one end of said bellcrank arm and having apivotal connection to a lever pivotally supported relative to the body,said portion of said suspension element being pivotally connected tosaid lever.
 6. A suspension system as set forth in claim 5 wherein theother portion of the suspension element is pivotally connected to thebell crank.
 7. A suspension system as set forth in any of claims 1 2, or6 through wherein the suspension element comprises a coil spring.
 8. Asuspension system as set forth in any of claims 1 2, or, 6 throughwherein the suspension element comprises a shock absorber.
 9. Asuspension system as set forth in claim 8 wherein the suspension elementfurther includes a coil spring surrounding the shock absorber.
 10. Asuspension system as set forth in claim 9 wherein the suspension systemis confined internally with an endless ground engaging track.